This invention relates to orthopedic surgery and more particularly to a drill guide and plate attachment mechanism for facilitating orthopedic surgical plating procedures.
Surgical plates in various forms have been used by orthopedic surgeons to fixate bones in a specifically desirable fashion or position such that bone knitting or healing occurs between the juxtaposed bony elements. In this regard, plating is employed across bony fracture sites or across surgical fusion sites to fixate and hold the bone components in a preferred configuration until solid bony union occurs. Because independent movement of the bony elements relative to each other retards or prevents bony union from occurring, bone fixation is frequently required, much like an external cast is used to inhibit motion sufficient to allow healing of a broken arm or leg bone.
The plate allowing fixation of the bony components is generally secured to the bone itself by the use of specifically designed bone screws. Drilling and tapping of bone is frequently required to allow the screws to be appropriately placed. Because surgical plating may be necessary in limited access approaches, drill guides are often used to limit the depth to which the bit itself violates bone, and to prevent injury to deep structures from the rotating drill. After drilling has occurred, the guide is frequently removed so that drilling and tapping of the drill hole can be performed. Once the hole has been drilled and the drill guide has been removed, it is often difficult to find the drill holes site deep within a body cavity. If drilling is done through the plate itself, removal of the guide to allow tapping of the hole and/or screw placement frequently allows sufficient plate movement that the drill hole site is difficult to find. This wastes valuable surgical time and is frustrating for the surgeon or his designate performing this component of the operation.
It would be desirable to have a drill guide which would allow drilling, tapping and screw placement to occur without having to remove, change or reposition the drill guide. It would also be desirable to have a drill guide which would securely hold the plate in position while drilling, tapping and screw placement is occurring.
An object of the invention is to provide an orthopedic drill guide and attachment mechanism which allows for easier and more accurate screw placement without having to remove or alter the position of the drill guide.
To achieve this end, three specific design alterations are required. The first requirement is that the drill guide attach to the plate external to the screw hole site. This is achieved by arms on the external surface of the tubular component of the guide. These arms are situated 180xc2x0 from each other and can be approximated either by forcing them together by an external tube slid over the internal tubular component of the drill guide or by a scissor mechanism external to the tubular component of the guide which approximates them.
The second design alteration occurs in the body of the plate itself and specifically at the site of the screw hole. To allow the guide arms to secure the plate, depressions or pits are formed at the sides of the screw hole to allow the external arms to grip and securely hold the drill guide to the plate, or in a double guide barrel design, grip the side of the plate.
By varying the lengths of the arms relative to each other, differing degrees of angulation of drilling and screw placement can occur. The arms can securely hold the plate in the appropriate position and attitude until all components of the fixation procedure have been completed (drilling, tapping, screw placement). Once the screw is secure, the plate is fixed in position and the arms can be disengaged and the drill guide can be removed. For the screw to securely hold the plate to the bone, the screw hole in the plate must be tapered such that a corresponding taper of the head of the screw holds the screw flush with the surface of the plate, or counter sunk to allow easy disengagement of the guide tube.
The third component of the design alteration related to the drills and taps employed with the drill guide. To function appropriately with the guide and plate, the drills and guides must be constructed such that the outer diameter of the shaft of the drill or tap fits snugly within the inner diameter of the drill guide. The actual drill bit or bone tap is of a small diameter which is equal to or less than the diameter of the smallest (deepest) component of the screw hole in the plate. This allows the drill or tap to be held securely while in use in the guide and also prevents drilling or tapping too deeply because the largest diameter of the drill or tap is always greater than the smallest diameter of the tapered screw hole in the plate.
In appropriate sequence, therefore, the plate can be gripped and held by the drill tube guide. Drilling and tapping and screw placement can safely and securely be carried out through the drill guide without need for alteration in position and the guide can be removed once the plate is securely fixed to bone.